Thermal Solution Research Articles

The thermal 'Buddha Board'-application of microstructured polyolefin films for variable thermal infrared transparency materials.

In this study, we explore the innovative application of biological principles of scattering foams and structural colouration of white materials to manipulate the transmission properties of thermal infrared (IR) radiation, particularly within the 8-14 μm wavelength range in polyolefin materials. Inspired by the complex skin of organisms such as chameleons, which can dynamically change colour through structural alterations, as well as more mundane technologies such as Buddha Boards and magic water colouring books, we are developing methods to control thermal IR transmission using common thermoplastic materials that are semi-transparent to thermal IR radiation. Polyethylene and polypropylene, known for their versatility and cost-effectiveness, can be engineered into microstructured sheets with feature sizes spanning from 5 to 100 μm. By integrating these precisely moulded microstructures with index-matching fluids, specifically IR transparent oils, we achieve a reversible modification of the thermal transmission properties. This novel approach not only mimics the adaptive functionality of natural systems but also offers a practical and scalable solution for dynamic thermal management. Our results indicate a promising pathway for the development of new materials that can adapt their IR properties in real time, paving the way for smarter thermal management solutions via radiative emission/absorption.

Low-cost scalable high-power-density solar thermochemical energy storage via accelerating ion diffusion in Calcium-based solid wastes

Calcium-based solar thermochemical energy storage (TCES) has a great potential for next-generation concentrated solar power (CSP) systems due to its unique advantages of high operation temperature from 750 ℃ to 900 ℃ and high energy storage density, while current Calcium-based pellets suffer from poor cyclic stability and slow reaction kinetics. The mainstream solution relies on expensive inert stabilizers and complicated fabrication processes, which severely limited their affordability and scalability. Herein, we propose a strategy for recycling different Ca-based solid wastes, achieving low-cost and scalable high-power-density solar TCES simultaneously via the synergistic effect of multiple solid wastes and MgCl2. The power density of proposed pellets is 2 times than that of the conventional CaCO3, as the promoted solid-state diffusion of Ca2+ accelerates the decomposition of CaCO3. The energy storage density is as high as 1191 kJ/kg after 50 cycles, along with energy storage economy higher than 70 MJ/$ and friction loss less than 0.3 %, far exceeding that of the state-of-the-art Calcium-based TCES pellets. The feasibility of high-performance solar-driven TCES is further demonstrated on a pilot-scale system, providing a promising high-temperature thermal energy storage solution for next-generation CSP techniques.

Multi-objective optimization design of high-pressure plate-fin ammonia boiler based on MO-SHERPA algorithm

With the rapid development of electrification, the high-pressure plate-fin ammonia boiler has been widely used as an effective thermal management solution, which has stimulated the demand for its structure design and optimization. The aim of this study was to establish a multi-objective optimization design method for high-pressure plate-fin ammonia boiler based on the hybrid and adaptive search strategy of MO-SHERPA and CFD simulation. Based on this method, a set of pareto-optimal solutions were obtained, and then the optimal configuration with lightest weight and high heat transfer performance was determined by calculating the deviation for weighted sum of comprehensive performance factor, entropy generation rate and structure weight. The effects of fin structural parameters of ammonia boiler were further examined on its performance. The results showed that increasing the spacing and height of offset strip fin and reducing its thickness could effectively improve the heat transfer performance. This study provides a theoretical method and some guidelines for the structural design of ammonia boiler with high operating pressure.

High-density thermal sensitivity maps of the body of people with multiple sclerosis: Implications for inclusive personal comfort systems

Inclusive thermal comfort solutions should accommodate the need of clinical groups such as people with Multiple Sclerosis (pwMS), who experience abnormal thermal sensitivity. The aim of this study was to develop high-density body maps of temperature sensitivity in pwMS to inform the design of patient-centred personal comfort systems.Fourteen pwMS (6 M/8 F; 48.6 ± 10.0 y) and 13 healthy individuals (CTR; 5 M/8 F; 47.8 ± 10.4) underwent a quantitative sensory test in a thermoneutral environment, during which they rated their local thermal sensations arising from the application of warm (39°C) and cold (27°C) stimuli to 115 bilateral body sites across the face, torso, upper and lower limbs. We used a z-transformation to create maps of hypo- and hyper-sensitivity for each individual MS participant using normative CTR data.We found that 50% of pwMS (N = 7/14) presented a loss of cold sensitivity over the upper limb, and a loss of warm sensitivity over the feet. Furthermore, 36% of pwMS (N = 5) presented warm hyper-sensitivity over the upper limb. Finally, cold sensitivity loss and warm sensitivity gain were more evenly distributed and affected a greater proportion of skin sites in MS (i.e. cold hypo-sensitivity = 44% of tested sites; warm hyper-sensitivity = 14%) than warm sensitivity loss (i.e. 10%), which was more focused on sites such as the feet.Our findings highlight the need to consider “thermosensory corrective power” when designing personal comfort systems, to accommodate either thermosensory loss or gain in pwMS. Our approach to clinical body mapping may support this process and help meeting the unique thermal needs of vulnerable individuals.

Limits of pressure-based ice detection during isochoric vitrification

Vitrification under isochoric (constant-volume or volumetrically confined) conditions has emerged as an intriguing new cryopreservation modality, but the physical complexities of the process confound straight-forward interpretation of experimental results. In particular, the signature pressure-based ice detection used in many isochoric techniques becomes paradoxical during vitrification, wherein the emergence of a sharp increase in pressure reliably indicates the presence of ice, but avoidance of this increase does not necessarily indicate its absence. This phenomenon arises from the rich interplay between thermochemical and thermovolumetric effects in isochoric systems, and muddies efforts to confirm the degree to which a sample has vitrified. In this work, we seek to aid interpretation of isochoric vitrification experiments by calculating thermodynamic limits on the maximum amount of ice that may form without being detected by pressure, and by clarifying the myriad physical processes at play. Neglecting kinetic effects, we develop a simplified thermodynamic model accounting for thermal contraction, cavity formation, ice growth, solute ripening, and glass formation, we evaluate it for a range of chamber materials and solution compositions, and we validate against the acutely limited data available. Our results provide both counter-intuitive insights— lower-concentration solutions may contract less while producing more pressure-undetectable ice growth for example— and a general phenomenological framework by which to evaluate the process of vitrification in isochoric systems. We anticipate that the model herein will enable design of future isochoric protocols with minimized risk of pressure-undetectable ice formation, and provide a thermodynamic foundation from which to build an increasingly rigorous multi-physics understanding of isochoric vitrification.

Thermal management of ultra high concentrator photovoltaic cells: Analysing the impact of sintered porous media microchannel heat sinks

Implementing advanced cooling strategies is essential to maintaining recommended operation conditions, enhancing energy efficiency, and extending the reliability of ultra-high concentrator photovoltaics. This study introduces a new application of sintered porous media as an effective and superior thermal management solution for ultra-high concentrator photovoltaic systems. Furthermore, predictive models for thermal and electrical performance are developed.A comprehensive three-dimensional computational fluid dynamics model was developed and verified against experimental work reported to investigate the performance of a novel sintered porous media for thermal management in ultra-high concentrator photovoltaics. Furthermore, the response surface methodology coupled with analysis of variance was used to analyze and comprehensively optimize the thermal management system. The main objective is to develop a predictive model for such systems equipped with a porous cooling system that predicts performance with a concentration ratio of up to 20000 Suns. Predictive models were formulated to outline the relationships between various independent variables: Reynolds number, concentration ratio, direct normal irradiance, wind speed, optical efficiency, fluid inlet temperature, and dependent performance metrics.This study highlights the effectiveness of sintered porous media in heat dissipation and efficiency enhancement in ultra-high concentrator photovoltaics thermal management. The results demonstrate that using sintered porous media compared to conventional channel heatsinks significantly enhances cell thermal management. Specifically, this approach reduces cell temperature by 15.3%, 8.97%, and 2% at concentration ratios of 20000, 10000, and 2000, respectively. Concurrently, implementing the new sintered porous media heatsink improves cell efficiency by 3.1%, 1.5%, and 0.3% for the same respective concentration ratio values.

Influence of Carboxymethyl Cellulose as a Thickening Agent for Glauber's Salt-Based Low Temperature PCM.

This work is focused on a novel, promising low temperature phase change material (PCM), based on the eutectic Glauber's salt composition. To allow phase transition within the refrigeration range of temperatures of +5 °C to +12 °C, combined with a high repeatability of melting-freezing processes, and minimized subcooling, the application of three variants of sodium carboxymethyl cellulose (Na-CMC) with distinct molecular weights (700,000, 250,000, and 90,000) is considered. The primary objective is to optimize the stabilization of this eutectic PCM formulation, while maintaining the desired enthalpy level. Preparation methods are refined to ensure repeatability in mixing components, thereby optimizing performance and stability. Additionally, the influence of Na-CMC molecular weight on stabilization is examined through differential scanning calorimetry (DSC), T-history, and rheology tests. The PCM formulation of interest builds upon prior research in which borax, ammonium chloride, and potassium chloride were used as additives to sodium sulfate decahydrate (Glauber's salt), prioritizing environmentally responsible materials. The results reveal that CMC with molecular weights of 250 kg/mol and 90 kg/mol effectively stabilize the PCM without phase separation issues, slowing crystallization kinetics. Conversely, CMC of 700 kg/mol proved ineffective due to the disruption of gel formation at its low gel point, hindering higher concentrations. Calculations of ionic concentration indicate higher Na ion content in PCM stabilized with 90 kg/mol CMC, suggesting increased ionic interactions and gel strength. A tradeoff is discovered between the faster crystallization in lower molecular weight CMC and the higher concentration required, which increases the amount of inert material that does not participate in the phase transition. After thermal cycling, the best formulation had a latent heat of 130 J/g with no supercooling, demonstrating excellent performance. This work advances PCM's reliability as a thermal energy storage solution for diverse applications and highlights the complex relationship between Na-CMC molecular weight and PCM stabilization.

Optimizing Renewable Energy Integration for Sustainable Fuel Production: A Techno-Economic Assessment of Dimethyl Ether Synthesis via a Hybrid Microgrid-Hydrogen System

This study offers an in-depth analysis and optimization of a microgrid system powered by renewable sources, designed for the efficient production of hydrogen and dimethyl ether—key elements in the transition toward sustainable fuel alternatives. The system architecture incorporates solar photovoltaic modules, advanced battery storage solutions, and electrolytic hydrogen production units, with a targeted reduction in greenhouse gas emissions and the enhancement of overall energy efficiency. A rigorous economic analysis was conducted utilizing the HYSYS V12 software platform and encompassing capital and operational expenditures alongside profit projections to evaluate the system’s economic viability. Furthermore, thermal optimization was achieved through heat integration strategies, employing a cascade analysis methodology and optimization via the General Algebraic Modeling System (GAMS), yielding an 83% decrease in annual utility expenditures. Comparative analysis revealed that the energy requirement of the optimized system was over 50% lower than that of traditional fossil fuel-based reforming processes. A comprehensive assessment of CO2 emissions demonstrated a significant reduction, with the integration of thermal management solutions facilitating a 99.24% decrease in emissions. The outcomes of this study provide critical insights into the engineering of sustainable, low-carbon energy systems, emphasizing the role of renewable energy technologies in advancing fuel science.

Evaluation of Energy Density in Hexadecane Phase Change Emulsions in Comparison to Water

The development of energy-dense, thermomechanically stable, and low-viscous phase change emulsions (PCMEs) is proposed as an alternative thermal energy storage solution for building air conditioning. A set of oil-in-water (O/W) nanoemulsions with hexadecane concentration varied between 10, 20, 25, 30, 35, and 40 wt. % is prepared and characterized with respect to their physical, thermal, and rheological properties. The storage characteristics are evaluated in terms of storage density, phase transition behaviour, supercooling, and dynamic viscosity. A systematic comparison in terms of energy density between the PCMEs and water is carried out at different temperature conditions. For this purpose, the storage break-even temperature TBE is proposed as a novel parameter to determine suitable operating temperature ranges and cycling conditions. The cycle stability is evaluated by rheological measurements, applying thermomechanical loads to the samples for a high number of cycles. According to the results, the energy density of the PCMEs is always higher than that of water, when the minimum temperature used for the cycling is below the storage break-even temperature. The emulsion with 30 wt. % hexadecane fraction is considered particularly promising, thanks to its high stability when exposed to thermomechanical stress, relatively low viscosity between 10 and 22 mPa s (0–30°C), and a storage density of 98 MJ/m3 within a cycling temperature range of 12 K.

Advancements in Battery Thermal Management for High-Energy-Density Lithium-Ion Batteries in Electric Vehicles: A Comprehensive Review

Lithium-ion batteries are frequently utilized in electric vehicles because of their high energy density and prolonged cycle life. Maintaining the right temperature range is crucial since lithium-ion batteries' performance and lifespan are highly sensitive to temperature. This study discusses a practical battery heat control system in this setting. The phenomenon of heat generation and significant thermal problems with lithium-ion batteries are reviewed in this work. The studies on various battery thermal management systems (BTMS) are then thoroughly analysed and arranged into groups based on thermal cycle possibilities. Direct refrigerant two-phase cooling, second-loop liquid cooling, and cabin air cooling are all components of the BTMS. Phase change material cooling, heat pipe cooling, and thermoelectric element cooling are all future parts of the BTMS. The maximum temperature and maximum temperature differential of the batteries are examined for each BTMS, and a suitable BTMS that addresses the drawbacks of each system is discussed. Finally, a novel BTMS is suggested as a practical thermal management solution for lithium-ion batteries with high energy density.

Advanced deep operator networks to predict multiphysics solution fields in materials processing and additive manufacturing

Unlike classical artificial neural networks, which require retraining for each new set of parametric inputs, the Deep Operator Network (DeepONet), a lately introduced deep learning framework, approximates linear and nonlinear solution operators by taking parametric functions (infinite-dimensional objects) as inputs and mapping them to complete solution fields. In this paper, two newly devised DeepONet formulations with sequential learning and Residual U-Net (ResUNet) architectures are trained for the first time to simultaneously predict complete thermal and mechanical solution fields under variable loading histories, process parameters, and even variable geometries. Two real-world applications are demonstrated: 1- coupled thermo-mechanical analysis of steel continuous casting with multiple visco-plastic constitutive laws and 2- sequentially coupled directed energy deposition for additive manufacturing. Despite highly challenging spatially variable target distributions, DeepONets can infer reasonably accurate full-field temperature and stress solutions several orders of magnitude faster than traditional and highly optimized finite-element analysis (FEA), even when FEA simulations are run on the latest high-performance computing platforms. The proposed DeepONet model’s ability to provide field predictions almost instantly for unseen input parameters opens the door for future preliminary evaluation and design optimization of these vital industrial processes.

Physically based heat exchanger sizing method for the thermal management system of all-electric regional aircraft

Fully electric propulsion systems integrating hydrogen-powered fuel cells and batteries are promising options to reduce the overall climate impact of regional aircraft. However, the increase in low-temperature heat sources aboard the aircraft calls for advanced thermal management system solutions. To address this challenge, this study presents a sizing methodology for ram air heat exchangers in the nacelle-integrated cooling loop of an all-electric regional aircraft based on the ATR-72 platform. Different discretization schemes are compared to identify an optimal sizing method. The results highlight the simplicity and efficiency of the 0D ε-NTU model. Geometric design variables are optimized with respect to drag and mass during a hot-day take-off. The resulting Pareto front reveals a tendency for low airflow outlet temperatures and large diffuser area ratios to result in lightweight designs but in turn, induce high drag and require a large installation space. Comparative analyses of specific optimal ram air duct designs and equivalent skin heat exchangers demonstrate the potential of a second heat sink over a flight mission. The limited heat transfer area of the skin heat exchanger proves insufficient for hot-day take-off and climb but offers advantages during cruise and descent thanks to the reduced drag.

Sub-ambient radiative cooling with thermally insulating polyethylene terephthalate aerogels recycled from plastic waste

We demonstrate that the aerogels produced from the polyethylene terephthalate (PET) fibers, recycled from plastic bottle wastes, can function both as a radiative cooler and a thermal insulator. An object under and in contact with the recycled PET aerogel is thermally insulated from the surroundings and, at the same time, cooled below ambient temperature via radiative cooling. These dual capabilities are tested under the warm sky of Singapore with more than 420 W/m2 downwelling. With a 0.48 cm thick recycled PET aerogel, a heat transfer coefficient of 1.67 W/m2·K is measured when the object underneath is cooled by 2 °C from ambient temperature. Even under a 4.5 cm thick recycled PET aerogel, completely opaque to the thermal emission and having a heat transfer coefficient less than 1 W/m2·K, a sub-ambient radiative cooling is observed. Our measured heat transfer coefficient is lower than that of other porous polymer materials or aerogels reported to date as a radiative cooling substrate. Our results demonstrate that the recycled PET aerogels are a multi-functional material, integrating radiative cooling and thermal insulation in a single substrate. Produced by processing waste materials, the recycled PET aerogels hold promise to be a highly scalable and sustainable thermal management solution, with a positive impact on the environment.

Detection of Fault in Solar Panel Using Thermal Image Processing

This paper explores the practical application of thermal cameras mounted on drones for thermal image processing in solar panel maintenance, with an emphasis on hotspot fault detection. Traditional manual inspection methods for solar panels are often time-consuming and labour-intensive, prompting the exploration of more efficient alternatives. By leveraging the capabilities of drones equipped with thermal cameras, high-resolution images and videos of solar panels can be captured swiftly and effectively. Advanced thermal image processing techniques are then employed to analyse these visuals, with a particular focus on identifying hotspot faults. The study introduces novel methodologies aimed at enhancing the accuracy and speed of anomaly detection in thermal imagery, thereby enabling proactive maintenance interventions. Real-time inspection capabilities integrated into the drone-based system provide immediate feedback to maintenance personnel, facilitating prompt decision-making and action. Through the adoption of this approach, solar panel maintenance operations are streamlined, leading to improved efficiency and cost-effectiveness. Ultimately, the implementation of drone-based thermal imaging solutions contributes to the sustainability and longevity of solar energy systems. Key Words: thermal image processing, solar panel, faults in solar panel, drones, hotspot, fault detection.

Investigating Advanced Building Envelopes for Energy Efficiency in Prefab Temporary Post-Disaster Housing

Prefabricated temporary buildings are a promising solution for post-disaster scenarios for their modularity, sustainability and transportation advantages. However, their low thermal mass building envelope shows a fast response to heat flux excitations. This leads to the risk of not meeting the occupant comfort and HVAC energy-saving requirements. The literature shows different measures implementable in opaque surfaces, like vacuum insulation panels (VIPs), phase change materials (PCMs) and switchable coatings, and in transparent surfaces (switchable glazing) to mitigate thermal issues, like overheating, while preserving the limited available internal space. This paper investigates the energy and overheating performance of the mentioned interventions by using building performance simulation tools to assess their effectiveness. The optimization also looks at the transportation flexibility of each intervention to better support the decision maker for manufacturing innovative temporary units. The most energy-efficient measures turn to be VIPs as a better energy solution for winter and PCMs as a better thermal comfort solution for summer.

Substrate dependence of the self-heating in lead zirconate titanate (PZT) MEMS actuators

Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators.

Analysing the Techno-Economic Viability of Different Solar Heating Systems in South African Beverage Plants

With ongoing real-term reductions in the cost of renewable energy technologies, opportunities to reduce carbon emissions within industry have improved. While the South African industrial sector has been investing in photovoltaics to meet electricity requirements, little has been done to replace fossil fuels used for the generation of process heat, representing two-thirds of the energy consumed. While previous studies have demonstrated the benefits and limitations of solar thermal (ST) energy solutions for industrial applications, recent developments in high-temperature heat pumps (HTHP) offer opportunities for novel configurations, including the use of renewable energy like photovoltaics (PV). This study compares the techno-economic benefits of solar thermal energy systems with PV-supported HTHP systems within the South African beverage sector. After a general consideration, simulation calculations are presented for selected applications. The cost of heat is determined for PV-heat pump systems operating on a stand-alone basis and with heat storage. The study finds that the levelised cost of heat of US$0.050-0.073/kWhth is at least twice that of coal-fired steam boilers. The study, therefore, calls for further work on optimising systems minimising steam requirements, and thereby improving the economics of heat pumps and for a coordinated effort to support the development and financing of high-temperature heat pumps for industrial applications.

The Human Insulin Thermal Solution project—a private sector initiative to address the thermostability of insulin

The Human Insulin Thermal Solution project—a private sector initiative to address the thermostability of insulin

An Ultralight Capillary-Driven Heat Pipe.

Capillary-driven heat pipes are an effective thermal solution for compacting electronic cooling systems. We advance such a heat pipe thermal solution with ultralightweighting for mobile applications. In our advancement, the envelope that encapsulates the phase-change process of a working fluid is fabricated via electroless plating being ∼40 μm thick. Furthermore, the wick structure that transports condensate to a heat source via capillarity is also electroless-plated onto the envelope's inner surfaces, creating a 100-μm-thick, microporous layer. This wick structure is sequentially superhydrophilized by blackening that forms a nanotexture on the microporous wick layer. An effective density of our prototype ultralight heat pipes (uHPs), as a measure of lightweighting, indicates, on average, a remarkable 73% weight reduction of commercial counterparts with sintered copper powder wick in similar exterior dimensions (e.g., ∼2.7 g, compared to ∼10.0 g) while providing equivalent heat spreading. Furthermore, the uHP operates at a 25% lower evaporator temperature, due to additional heat rejection to the surroundings through the ultrathin-walled envelope and wick.

Reduced temperature in lateral (AlxGa1−x)2O3/Ga2O3 heterojunction field effect transistor capped with nanocrystalline diamond

The low thermal conductivity of β-Ga2O3 is a significant concern for maximizing the potential of this ultra-wide bandgap semiconductor as a power switching device technology. Here, we report on the use of nanocrystalline diamond (NCD) deposited via microwave plasma enhanced chemical vapor deposition (MP-CVD) as a top-side, device-level thermal management solution on a lateral β-Ga2O3 transistor. NCD was grown via MP-CVD on β-(AlxGa1−x)2O3/β-Ga2O3 heterostructures prior to the gate formation of the field-effect transistor. A reduced growth temperature of 400 °C and a SiNx barrier layer were used to protect the oxide semiconductors from etching in the MP-CVD H2 plasma environment. Raman spectroscopy showed a highly sp3-bonded NCD film was obtained at 400 °C, with grain size of about 50–100 nm imaged via atomic force microscopy. The incorporation of the NCD heat-spreading layer resulted in a β-(AlxGa1−x)2O3/β-Ga2O3 heterostructure field-effect transistor showing a decrease in the total thermal resistance at the gate by 42%. The fabrication process, including the NCD etch in the gate region, will need to be improved to minimize the impact of these processes on important device characteristics (i.e., drain current, threshold voltage, and leakage current).